1. Field of the Invention
The present invention relates to a method for manufacturing a toner, a toner obtained by the production method, a developer containing the toner, a developing device using the developer, and an image forming apparatus.
2. Description of the Related Art
Conventionally, a surface modification treatment for coating the surface of powder particles with a coating material has been carried out in order to improve characteristics of the powder particles such as toner particles.
As a method for the surface modification treatment of the powder particles such as toner particles, a method is known that a mechanical stirring force is applied to the powder particles by a rotary stirring section such as a screw, blade, or rotor to fluidize the powder particles in a powder passage and a coating material is ejected from a spray nozzle to the powder particles in a fluid state.
In the surface modification treatment method, a method of covering a surface of power particles with a coating material contained a liquid by spraying the liquid from a spray nozzle is disclosed in Japanese Examined Patent Publication JP-B2 5-10971 (1993). Specifically, powder particles are fluidized by rotating a rotary stirring apparatus in a peripheral speed of 5 to 160 m/sec, and a liquid is sprayed to the powder particles under the fluidized state from a spray nozzle. This method can fix and form a film of a coating material constituting fine solid particles contained in a liquid or the liquid onto the surface of the powder particles. According to the method disclosed in JP-B2 5-10971, adhesion between the coating material and the powder particles can be increased, and additionally, time required in the surface modification treatment can be shortened.
Further, Japanese Unexamined Patent Publication JP-A 4-211269 (1992) discloses a method for manufacturing a microcapsule in which resin particles are adhered to the surface of inner core particles and are treated with a solvent that dissolves the resin particles to form a coating layer on the surface of the inner core particles. The method for manufacturing a microcapsule disclosed in JP-A 4-211269 comprises at least a step of adhering the resin particles to the surface of the inner core particles, a step of treating resin particles with a solvent that dissolves the resin particles, and a step of drying and recovering the treated particles.
However, the method disclosed in JP-B2 5-10971 has the following problem. In the case that powder particles are fluidized by applying mechanical stirring force in a rotary stirring apparatus and a liquid containing a coating material is sprayed to the powder particles in the fluidized state, powder particles must be fluidized in an isolated state in order to obtain covered particles comprising the powder particles uniformly coated with the coating material. To fluidize the powder particles in an isolated state, a peripheral speed of the rotary stirring apparatus must be increased to a certain extent. However, where the peripheral speed of the rotary stirring apparatus is increased, a fluidizing speed of the powder particles is increased, and frequency that the powder particles collide with an inner wall of an apparatus is increased. Where the frequency that the powder particles collide with an inner wall of an apparatus is excessively increased, the problem arises that the powder particles are easily adhered to the inner wall of an apparatus, and other powder particles and coating material aggregate and grow by acting the adhered powder particles as nuclei. Where the powder particles and the coating material aggregate and grow on the inner wall of an apparatus, the powder particles fluidize. This gives rise to the problem that flow passage is narrowed, thereby preventing fluidization in an isolated state and the problem of decrease in yield.
Since the treatment is carried out by the use of the solvent that dissolves a resin of the resin particles in the method disclosed in the JP-A 4-211269, the solvent taken in the resin of the resin particles hardly vaporizes and a large amount of the aggregate is generated even when the inner core particles and the resin particles are fluidized at high speed. Further, large amounts are adhered to the inner wall of the apparatus, which are difficult to be recovered in a state of primary particles, and the method does not provide excellent productivity. There is a possibility that some kinds of solvents dissolve even the inner core particles so that waxes contained in the inner core particles and the like are adhered and exposed to the surface of the inner core particles as particles, and when using the obtained microcapsule particles as a toner, toner performance including storing performance and fixing performance of the toner is deteriorated.